Traxxas Stampede 4x4 VXL Top Speed Run

I strapped a gps to the back of my Traxxas Stampede 4x4 VXL to test the top speed. Top speed so far is 38.6 mph. I'm a little disappointed. With better tires and different gearing it will go faster. I'm running a Castle Creations Mamba Max Pro SCT ESC and Neu-Castle 1415-2400kv motor combo, SPC 11.1 volt 5000mah 3s lipo battery, 17 tooth pinion, 54 tooth spur gear, and 4.9" Pro-Line Masher 2000 tires.